Most of the Derby horses every year descend from a stallion born in the late 1950s or early 1960s, for that matter.
Ooh, couldn’t find that, found this instead:
Almost All Modern Horses Descended From A Few Oriental Stallions
GrrlScientist
Senior Contributor
Evolutionary & behavioural ecologist, ornithologist & science writer
https://www.forbes.com/sites/grrlscientist/2017/07/10/almost-all-modern-horses-descended-from-a-few-oriental-stallions/?sh=34fd261e16c5
Foaled in Great Britain in 1853, Bonnie Scotland came to Belle Meade Mansion in Nashville, Tennessee, in 1872, at the age of 19. Even though he died at Belle Meade in February 1880, he was named the outstanding sire of that year. Here is a short listing of some of the pedigreed horses from his line: Bramble, 1875, earned $32,660; Man-O-War, 1917, earned $249,465; Prince Rose, 1928, earned $59,267; Sea Biscuit, 1933, earned $437,730; War Admiral 1934, earned $273,240; Secretariat, 1970, earned $1,316,808; Seattle Slew, 1974, earned $1,208,726; and Affirmed, 1975, earned $2,393,818.
https://www.crossville-chronicle.com/news/local_news/pedigree-of-derby-winners/article_9dbd72f6-10e1-5335-a8e0-58e718b40bda.html